Process for producing electrode binder pitch and carbon black feedstock

ABSTRACT

There is disclosed a process for converting the residue portion of a cracked petroleum product into electrode binder pitch and carbon black feedstock, both more valuable products, by heat soaking the residue to produce electrode binder pitch and a middle distillate, and blending the middle distillate with some of the electrode binder pitch to produce a carbon black feedstock.

United States Patent 1 Roza June 27, 1972 [54] PROCESS FOR PRODUCING[56] References Cited ELECTRODE BINDER PITCH AND UNITED ATE A T CARBONBLACK FEEDSTOCK ST SP 5 2,752,290 6/1956 Beattie ..208/40 [72] Inventor:Abraham Gerrit Alexander Roza, Amster- 2,992,181 W196] Renne,Netherlands, 3,412,009 11/1968 Smith et al ..208/72 [73] Assignee: ShellOil Company, New York, N.Y. Primary Examiner Delben E Gamz [22] Filed:Sept. 29, 1969 Assistant Examiner-G. E. Schmitkons A -l-l kl pp No:862,025 ttorney aroldL Den er and GlenR Grunewald [57] ABSTRACT ForeignApplication Priority Dim There is disclosed a process for converting theresidue portion 3 of a cracked petroleum product into electrode binderpitch Oct. 3, 1968 Great Br1tam ..46,9l5/68 and carbon black feedstockboth more valuable products y heat soaking the residue to produceelectrode binder pitch [52] Cl 53 47 and a middle distillate, andblending the middle distillate with f b k 511 Int. Cl. ..c1o 3/04, ClOg37/04, ClOg 37/08 2232,2 electmde p'tch pmduce a car mac [58] Field ofSearch ..208/7 1 76, 40, l3]

13 Claims, No Drawings PROCESS FOR PRODUCING ELECTRODE BINDER PITCH ANDCARBON BLACK FEEDSTOCK BACKGROUND The starting material for thepreparation of carbon black, the so-called carbon black feedstock,hereinafter CBF, consists of a high boiling material with a higharomaticity. This high aromaticity should not be due substantially tothe presence of a high percentage of residual material, because it isoften very difficult to prepare carbon black of the requisite structurefrom residual material. The aromaticity of CBF is generally expressed inthe Bureau of Mines Correlation Index (Cl), represented by the formulaCI= 48,640/K 473.7 G 456.8 where K temperature in K at which 50 percentv distillate has been obtained during a distillation of the materialaccording to ASTM D 158, and G density of the material at 60 F. relativeto water of 60 F.

To be suitable for use as CBF, the material should preferably have a CIof at least 120. The amount of coking residue of CBF, expressed in theConradson Carbon Residue (CCR), should preferably be below 12 percent w.The material should have a flash point (determined according to thePensky Martin closed cup method) of at least 65 C. A sufficiently highflash point is required to obviate difi'lculties in the processing ofthe material. The requirement concerning flash point is easily satisfiedif a material withan initial boiling point of 200 C or higher is chosenas CBF. It should be noted that the requirements of the variouscarbon-black manufacturers with regard to the CBF vary rather widely.CBF is frequently evaluated on the basis of performance so that in somecases products which do not fully come up to the above-mentionedrequirements may still be acceptable for certain carbon-blackmanufacturers. Products which completely satisfy the abovementionedrequirements may be expected to be acceptable in all respects forcarbon-black preparation. Suitable base materials for the preparation ofcarbon black on the basis of petroleum are bottom products obtained bycracking of hydrocarbon oils.

Electrode binder pitch, hereinafter EBP, is used as a binder for carbonelectrodes which find application in the chemical and metallurgicalindustries, such as the preparation of aluminum from A1 Large quantitiesof electrode are required especially for this application, because thecarbon electrode combines with the oxygen of the A1 0 and is consumedduring the electrolysis. Carbon electrodes are baked at an elevatedtemperature from a mixture of about 70-90 percent w coke and about 10-30percent w pitch. The pitch should meet a number of requirements in orderto be suitable for this purpose. The pitch must have a high cokingresidue (CCR at least 40 percent w). The coke formed from the pitch musthave a good binding power towards the coke that was already present inthe mixture before baking. To have such properties the pitch should havea high content of high-molecular weight aromatic compounds which areinsoluble in toluene, but soluble in quinoline, the said content beingpreferably at least 15 percent w. As the pitch has to be mixed in theliquid state with the coke before baking, there is a strong preferencefor pitches whose softening point is below 120 C. Only pitches with ahigh aromaticity have the above-mentioned properties.

As it has been found in the preparation of aluminum that inorganicconstituents, in particular iron and vanadium compounds, considerablyincrease the electrode consumption per ton of aluminum produced, the ashcontent of a good EBP that is suitable for use in the manufacture ofelectrodes for the preparation of aluminum should be less than 0.1percent w.

The starting material for the preparation of EBP is coal tar in manycases. It is also possible to prepare suitable EBP from petroleum,namely from bottom products or residues obtained by cracking ofhydrocarbon oils. These bottom products generally contain too fewcomponents that are insoluble in toluene to be suitable per se as EBP.In order to render the bottom products suitable for this purpose, thecontent of components that are insoluble in toluene should be increased.This can be achieved by subjecting the bottom products to a heatsoaking. For the preparation of an EBP with the desired softening pointthe bottom products should in general be distilled after the heatsoaking.

From the above it will be clear that bottom products obtained bycracking of hydrocarbon oils may be used both as CBF and for thepreparation of EBP. If these bottom products are used for thepreparation of EBP, great quantities of middle distillate are obtainedin addition to EBP. Middle distillate is a hydrocarbon fraction boilinghigher than gasoline, but still not the highest boiling of thevaporizable hydrocarbon materials. Middle distillate usually boilsbetween about 200 C. and about 400 C., but may have a substantiallyhigher initial boiling point, e.g., 270 C. This distillate can inprinciple be used only as fuel oil and has considerably less value thanEBP or CBF. It does not therefore appear economically justifiable tosubject a base material that is per se suitable as CBF to an additionalheat soaking which yields not only a certain quantity of valuable EBPbut also a large amount of low'value middle distillate.

THE INVENTION It has now been found that it is possible to prepare bothCBF and EBP from the above-mentioned bottom products without obtaininglow-value middle distillate. To this end, a hydrocarbon oil which hasbeen subjected to cracking is used as starting material. In accordancewith this invention, the bottoms, or the heaviest pan of the crackedproduct, is subjected to a heat soaking to increase the proportion ofcomponents that are insoluble in toluene. A middle distillate and an EBPwith the desired softening point are separated from the productsobtained by heat soaking. The middle distillate so obtained issubsequently blended with a small quantity of the EBP prepared in orderto enhance the aromaticity of the distillate thereby preparing a productthat is suitable as CBF. lf the feed for the heat soaker has arelatively high initial boiling point, middle distillate can beseparated from the remaining part of the cracked product, and used forthe preparation of CBF. In that case the cracked product middledistillate is blended with the middle distillate obtained from the heatsoaker and with a small quantity of the EBP prepared.

The invention therefore relates to a process for the preparation of bothEBP and CBF by cracking a hydrocarbon oil as hereinafter defined andseparating a residual fraction from the cracked products, subsequentlyexposing said residual fraction to a heat soaking as hereinafter definedand separating an EBP from the heat soaking products, and finallyblending a part of the resultant electrode binder pitch with at least apart of a middle distillate separated from the heat soaking products toproduce a CBF.

Whenever cracking or heat soaking are referred to in the presentapplication, these terms should be understood to mean the following:

Cracking is the exposure of a feed to a high temperature for arelatively short time to convert a substantial part of the feed intoproducts boiling below the initial boiling point of the feed.

Heat soaking is the exposure, in substantially liquid state, of a bottomproduct, from a cracking plant to an elevated temperature for arelatively long time to increase the aromaticity and the content ofcompounds that are insoluble in toluene,

Cracking processes yielding bottom products that are very suitable asfeedstock for the preparation of both EB! and CBF according to theinvention include, among others, the following thermal crackingprocesses which are carried out at temperatures above 400 C.

a. Thermal cracking at a temperature above 750 C. of either petroleumdistillates boiling between 50 and 200 C. or petroleum distillatesboiling between 170 and 370 C. to prepare gases that may serve as basematerial for the petrochemical industry.

b. Thermal cracking of cycle oil, possibly together with slurry oil,obtained in the preparation of gasoline by catalytic cracking ofpetroleum distillates boiling between 170 and 500 C.

c. Thermal cracking of heavy distillates boiling between 350 and 500 C.,which are obtained in the distillation under reduced pressure ofresidues originating from atmospheric distillation of crude oil.

The cracking processes mentioned under (b) and (c) are as a rule carriedout at temperatures between 450 and 550 C.

The initial boiling point of the residual fraction of the crackedproducts that is suitable for use as feedstock for the heat soaker isdetermined by the following considerations:

a It is often impossible to separate cracked products boiling below300-350 C. as liquid bottom product, in particular in the case ofcracking processes operated above 750 C., where the feed is cracked inthe gaseous state under elevated pressure.

b. If a larger proportion of the cracked products is subjected to theheat soaking, the yield of EBP relative to the total quantity of crackedproducts obtained will increase because heavier molecules are formedthrough polymerization of relatively light material during the heatsoaking. From cracked products with a boiling point below 250 C.,however, only very little heavy material that may form a suitablecomponent of EBP will be produced during the heat soaking. Crackedproducts with boiling points below 150 C. will make hardly anycontribution to the formation of CBF or EBP during the heat soaking. Ifall cracked products with boiling points above 150 C. are subjected tothe heat soaking, the yield of CBF and EBP relative to the totalquantity of cracked products obtained will be a maximum. However,substantially the same yield can be obtained if the heat soaking isapplied only to cracked products boiling above 250 C.

c. As the initial boiling point of the heat-soaker feedstock is lower, ahigher pressure will have to be applied during the heat soaking toprevent the loss of the light material. The operation at higher pressureinvolves higher running costs of the process.

(1. 1f the heat-soaker feedstock is too heavy and viscous, there is therisk of coke deposition during heat soaking and clogging may occur. Itis therefore advisable to choose the initial boiling point of theheat-soaker feed to be not higher than 400 C.

These considerations lead to the choice of the heaviest part of crackedproducts with an initial boiling point between 150 and 400 C., andpreferably between 250 and 400 C., as feedstock for heat soaking, inorder to secure the highest possible yield of CBF and EBF withoutdifficulties in the operation of the process.

When heat soaking is carried out at lower temperatures, a longer timewill be required. For instance, heat soaking at 450 C. for minutesproduces a final liquid product with substantially the same propertiesas one obtained by heat soaking at 350 C. for 25 hours. If heat soakingis carried out at temperatures below 350 C., extremely long times arenecessary. At higher heat soaking temperature the risk of cokedeposition in the heat soaker increases and higher pressure is requiredto prevent the loss of some of the feedstock during heat soaking.

In view of the above-mentioned considerations, the heat soaking can beconveniently carried out at a temperature between 350 and 500 C.,preferably between 400 and 450 C., for at most 2 hours. If the heatsoaking is carried out under dehydrogenating conditions, which can bebrought about by passing air through the liquid during heat soaking, aconsiderably shorter residence time is required. If air is passedthrough the liquid during the heat-soaking process, temperatures below400 C. may be used without long residence times. When using air, theheat soaking is best carried out at atmospheric pressure and to obviateformation of great quantities of distillate during heat soaking, abottom product with an initial boiling point above 350 C. should be usedas heatsoaker feedstock.

During heat soaking gases and distillate boiling below the initialboiling point of the heat-soaker feed are formed, and these tend toescape. The distillate will remain wholly or in part in the heat soakerdepending on the pressure applied, but the material in the heat soakerat the conclusion of the heat soaking usually must be distilled toprepare an E8? with the desired softening point. If the heat soaking isconducted with air, it may be attractive to choose the operatingconditions such that an EBP with the desired softening point is retainedin the heat soaker, by allowing a certain quantity of distillate toescape from the heat soaker with the gases vented from the heat soaker.

In general, the distillation of the products obtained by heat soaking isconducted to yield both an EBP and a middle distillate. The middledistillates obtained from this process may be used wholly or in part forthe preparation of CBF.

If the heat soaking is conducted with air in such a fashion that an EBPwith the desired softening point remains behind in the heat soaker, itmay be necessary to blend a part of this EBP exclusively with a middledistillate obtained from the cracked products rather than the middledistillate produced by heat soaking.

The flash point of the CBF should preferably be not lower than 65 C.,and accordingly, the middle distillate used for the preparation of CBFshould likewise have a flash point not lower than 65 C. Middledistillates with an initial boiling point of 200 C. or higher easilysatisfy this requirement.

If the residual fraction that is separated from the cracked products andsubjected to heat soaking has an initial boiling point well above 200C., it is advisable to separate a middle distillate from the crackedproducts and use it as well as the middle distillate produced in heatsoaking for the preparation of CBF, in order to ensure an adequate yieldboth of EBP and CBF.

The invention may be better understood with the aid of the followingexamples.

EXAMPLE I A cycle oil obtained by the catalytic cracking at 460 C of ahydrocarbon oil boiling between 340 and 450 C. was thermally cracked at492 C. The products obtained by this thermal cracking process E wereseparated by distillation into a light distillate fraction and a heavyresidual fraction A. The cutting point between the two fractions was 250C. Fraction A was subjected to heat soaking at 400 C. at a pressure of 5atm for 15 hours, which caused 2.6 percent by weight of gas to escape.The material present in the heat soaker at the conclusion of the heatsoaking was split by distillation into 7.2 percent by weight of a lightdistillate fraction, 59.2 percent by weight of a middle distillatefraction D and 31.0 percent by weight of EBP. The cutting point betweenthe two distillate fractions was 200 C. The EBP so obtained had thefollowing properties:

Softening point Ring and Ball Fraction D was blended with 8.0% by weightof EBP to obtain a CBF with the following properties:

Cl: CCR:

Flash Point: 82C

in this way the following products were obtained from the crackedproducts boiling above 250 C:

2.6 percent w gas 7.2 percent w light distillate 67.2 percent w CBF 23.0percent w EBP EXAMPLE II The cracked products E mentioned in Example Iwere separated by distillation into three fractions, namely a lightdistillate fraction, a middle distillate fraction B and a heavy residualfraction C. The cutting point between the two distillate fractions was250 C. and that between fractions B and C 350 C. The quantities offractions B and C amounted to 33.8 and 66.2 percent by weight. FractionC was subjected to heat soaking at 450 C. and atm pressure for 1% hourswhich caused 2.l percent by weight of gas to escape. The materialpresent in the heat soaker at the conclusion of the heat soaking wassplit by distillation into 3.4 percent by weight of a light distillatefraction, 31.5 percent by weight of a middle distillate fraction D and29.2% by weight of EBP. The cutting point between the two distillatefractions was 200 C. The BB? so obtained had the following properties:

Softening point Ring and Ball 102C Content of. components which are insoluble in toluene, but soluble in quinoline 23.2%w

CCR

Fraction B was blended with fraction D and with 10.9 percent by weightof EBP to obtain a CBF with the following properties:

Cl: 121 CCR: l l.0%w Flash point: 102C EXAMPLE Ill The cracked productsE mentioned in Example I were separated by distillation into a lightdistillate fraction and a heavy residual fraction A. The cutting pointbetween the two fractions was 350 C. Fraction A was subjected to heatsoaking at 450 C. and 15 atm pressure for 1% hours which caused 3.2percent by weight of gas to escape. The material present in the heatsoaker at the conclusion of the heat soaking was split by distillationinto 5.1 percent by weight of a light distillate fraction, 47.6 percentby weight of a middle distillate fraction D and 44.1 percent by weightof EBP. The cutting point between the two distillate fractions was 200C. The BB? so obtained had the following properties:

Softening point Ring and Ball 102C Content of components which are insoluble in toluene, but soluble in quinoline 23.2%w

CCR 52.0%w

Fraction D was blended with 5.6 parts by weight of EBP to obtain a CBFwith the following properties:

CI: 125 CC R: 8.5%w Flash point: 98C

In this way the following products were obtained from the crackedproducts boiling above 350 C:

3.2 percent w gas 5. 1 percent w light distillate 53.2 percent w CBF38.5 percent w EBP As fraction A accounts for 66.2 percent w of thecracked products boiling above 250 C., the yields relative to thecracked products boiling above 250 C. are as follows:

2.1 percent w gas 3.4 percent w light distillate 35.2 percent w CBF 25.5percent w B8? EXAMPLE IV The cracked products E mentioned in Example Iwere split by distillation into a light distillate fraction, a middledistillate fraction B and a heavy residual fraction C. The cutting pointbetween the two distillate fractions was 250 C. and that betweenfractions B and C was 375 C. The quantities of fractions B and Camounted to 39.2 and 60.8 percent by weight, respectively. Fraction Cwas subjected to heat soaking at 375 C. and atmospheric pressure for 2hours and 20 minutes, while liters of air per kg feed was passed throughit. During this heat soaking 12.4 percent by weight of gaseous productsand distillate escaped from the heat soaker. The part of this gaseousproduct that was liquid at room temperature was added to the materialpresent in the heat soaker at the conclusion of the heat soaking, andthe resultant product was subsequently split by distillation into 2.2percent by weight of a light distillate fraction, 24.2 percent by weightof a middle distillate fraction D and 33.5 percent by weight of EBP. Thecutting point between the two distillate fractions was 200 C. The BB? soobtained had the following properties:

Softening point Ring and Ball 94C Content of components which are insoluble in toluene,

but soluble in quinoline 23.9%w

CCR 50.5%w

Fraction B was blended with fraction D and with 12.6 percent by weightof EBP to obtain a CBF with the following properties:

Cl: l 26 CCR: 8.6%w Flash point: 88C.

In this way the following products were obtained from the crackedproducts boiling above 250 C.:

1.0 percent w gas 2.2 percent w light distillate 75.9 percent w CBF 20.9percent w EBP Comparison of the results reported in Examples 1 and llshows that heat soaking of all cracked products boiling above 250 C.yields little more EBP than heat soaking of the cracked products boilingabove 350 C. (31.0 and 29.2% by weight, respectively, in both cases onthe basis of cracked product boiling above 259 C.).

Comparison of the results reported in Examples ll and III shows that ifthe fraction with a boiling range between 250 and 350 C. from thecracked product is not used for the preparation of CBF, a higher yieldof EBP is obtained, whereas the yield of CBF drops to an appreciablylower level.

Comparison of the results reported in Examples l and IV shows that bypassing air through the liquid during heat soaking, substantially thesame effect can be reached in a considerably shorter time.

EXAMPLE V A hydrocarbon oil boiling between 65 and C. was thermallycracked at a temperature of 800 C. with the aid of superheated steam.From the products so obtained a heavy residual fraction A with aninitial boiling point of 300 C. was separated. Fraction A was subjectedto heat soaking at 370 C. and a pressure of 3 atm for 26 hours. Thiscaused 2.8 percent by weight of gas to escape. The material present inthe heat soaker at the conclusion of the heat soaking was split bydistillation into 3.2 percent by weight of a light distillate fraction,44.0 percent by weight of a middle distillate fraction D and 50.0percent by weight of EBP. The cutting point between the two distillatefractions was 200 C. The EBP had the following properties:

Softening point Ring and Ball 98C Content of Components which are insoluble in toluene, but soluble in quinoline 23.5%w

CCR 1.0%w

Fraction D was blended with l 1.0 percent by weight of EBP to obtain aCBF with the following properties:

Cl: 128 CCR: l0.9%w Flash point: 95C

In this way the following products were obtained from the crackedproducts boiling above 300 C.

2.8 percent w gas 3.2 percent w light distillate 55.0 percent w CBF 39.0percent w EBP EXAMPLE VI A hydrocarbon oil boiling between 250 and 350C. was thermally cracked at a temperature of 780 C. with the aid ofsuperheated steam. From the products so obtained (F) a heavy residualfraction A with an initial boiling point above 330 C. was separated.Fraction A was subjected to heat soaking at 440 C. and a pressure of 15atm for 24 minutes. This caused 6.2 percent by weight of gas to escape.The material present in the heat soaker at the conclusion of the heatsoaking was split by distillation into 3.6 percent by weight of a lightdistillate fraction, 28.3 percent by weight of a middle distillatefraction D and 61.9 percent by weight of EBP. The cutting point betweenthe two distillate fractions was 200 C. The EBP so obtained had thefollowing properties:

Softening point Ring and Ball 92C Content of components which are insoluble in toluene, but soluble in quinoline 20.2%w

CCR 49.0%w

Fraction D was blended with 6.0 percent by weight of EBP to obtain a CBFwith the following properties:

Cl: l 25 CC R: 9.8%w Flash point: 90C

In this way the following products were obtained from the crackedproducts boiling above 330 C.:

6.2 percent w gas 3.6 percent w light distillate 34.3 percent w CBF 55.9percent w EBP EXAMPLE VII From the cracked product F mentioned inExample VI a heavy residual fraction with an initial boiling point of330 C. was separated. This fraction was split by distillation into amiddle distillate fraction B and a heavy residual fraction C. Thecutting point between the two fractions was 400 C. The quantities offractions B and C amounted to 32.3 and 67.7 percent by weight,respectively. Fraction C was subjected to heat soaking at 375 C. andatmospheric pressure for 3 hours, while liters air per kg feed waspassed through it. During this heat soaking 43. percent by weight ofgaseous products and distillate escaped from the heat soaker. Thematerial present in the heat soaker at the conclusion of the heatsoaking was an EBP with the following properties:

Softening point Ring and Ball l00C Content of components which are insoluble in toluene, but soluble in quinoline 22.2%w

CCR 51.2%w

Fraction B was blended with 7.9 percent by weight of EBP to obtain a CBFwith the following properties:

or; 129 CCR: 1 1.5%w Flash point: 187C 350 and 500 C., separating anelectrode binder pitch from I the heat soaking products, and blending apart of said electrode binder pitch with middle distillate separatedfrom said cracked products or from said heat soaking products to form acarbon black feedstock.

2.. The process of claim 1 wherein the residual fraction separated fromthe cracked product has an initial boiling point between 250 and 400 C.

3. The process of claim 1 wherein the heat soaking is carried out undera pressure above atmospheric at a temperature between 400 and 450 C. for2 hours at most.

4. The process of claim 1 wherein the heat soaking is carried out at atemperature between 350 and 400 C., while air is passed through theliquid.

5. The process of claim 4 wherein the heat soaking is carried out underatmospheric pressure and enough air is passed through the liquid toremove light material so that an electrode binder pitch with the desiredsoftening point remains behind in the heat soaker as a residue.

6. The process of claim 5 wherein the heat soaking is applied to aresidual fraction with an initial boiling point above 7. The process ofclaim 1 wherein the cracking is carried out at a temperature between 450and 550 C.

8. The process of claim 1 wherein cracking is carried out at atemperature above 750 C. I

9. The process of claim 1 wherein a catalytic cracker cycle oil iscracked.

10. The process of claim 1 wherein a petroleum distillate boilingbetween 350 and 500 C. is cracked.

11. The process of claim 1 wherein a petroleum distillate boilingbetween and 370 C. is cracked.

12. The process of claim 1 wherein a petroleum distillate boilingbetween 50 and 200 C. is cracked.

13. The process of claim 1 wherein the middle distillate used for thepreparation of carbon black feedstock has a flash point of at least 65C.

2. The process of claim 1 wherein the residual fraction separated fromthe cracked product has an initial boiling point between 250* and 400*C.
 3. The process of claim 1 wherein the heat soaking is carried outunder a pressure above atmospheric at a temperature between 400* and450* C. for 2 hours at most.
 4. The process of claim 1 wherein the heatsoaking is carried out at a temperature between 350* and 400* C., whileair is passed through the liquid.
 5. The process of claim 4 wherein theheat soaking is carried out under atmospheric pressure and enough air ispassed through the liquid to remove light material so that an electrodebinder pitch with the desired softening point remains behind in the heatsoaker as a residue.
 6. The process of claim 5 wherein the heat soakingis applied to a residual fraction with an initial boiling point above350* C.
 7. The process of claim 1 wherein the cracking is carried out ata temperature between 450* and 550* C.
 8. The process of claim 1 whereincracking is carried out at a temperature above 750* C.
 9. The process ofclaim 1 wherein a catalytic cracker cycle oil is cracked.
 10. Theprocess of claim 1 wherein a petroleum distillate boiling between 350*and 500* C. is cracked.
 11. The process of claim 1 wherein a petroleumdistillate boilinG between 170* and 370* C. is cracked.
 12. The processof claim 1 wherein a petroleum distillate boiling between 50* and 200*C. is cracked.
 13. The process of claim 1 wherein the middle distillateused for the preparation of carbon black feedstock has a flash point ofat least 65* C.